1. Field of the Invention
The present invention relates to: an ultradispersed one of primary particles of nanometer-sized carbon (hereinafter referred to as “nanocarbon”); a method of manufacturing the ultradispersed primary particle of the nanocarbon; techniques and/or their practical applications for preventing these primary particles of the nanocarbon from recombining with each other after they are ultradispersed.
2. Description of the Related Art
In the era of nano-technology or of ultimate High Technology, it is one of the most important issues to establish fundamental techniques for manufacturing, evaluating, measuring, reserving and appropriately treating a nanometer-sized material having a diameter of approximately 10−9 meter.
In general, methods for manufacturing the nanometer-sized material are classified into two categories: one of which is a so-called “bottom-up or build-up method”; and, the other is a so-called “top-down or break-down method”.
In the bottom-up method: a starting material is the minimum-sized material such as an atom or a molecule; atoms and molecules are then permitted to combine with each other by their self-organizing mechanism and like mechanisms to become bigger in size step by step.
On the other hand, in the top-down method, a starting material is a relatively large bulk or mass of material, which is gradually broken down into smaller pieces in size by grinding, crushing, cutting and like pulverizing processes.
In any one of these methods, regardless of the types of material, when the material reaches an approximately nanometer-sized particle, these particles begin to combine with each other by their self-organizing mechanism to grow up to an assembly having a diameter of from approximately several micrometers to approximately several millimeters, in general. In contrast with an assembly or aggregate structure of conventional fine particles, the assembly or an aggregate structure of the nanometer-sized particles looks like a solid cluster in behavior once the assembly has been formed. Such assembly of the nanometer-sized particles is hard to break down and operates as a single large solid particle, so that it is difficult for the primary particle of nanometer-sized carbon to present its own functional properties. Due to this, the self-organizing mechanism of the nanometer-sized particle is a fatal obstacle to development of the fundamental techniques in the field of nano-technology. However, there is still not found an essential solution for this problem in the prior art. Consequently, in the prior art, in order to prevent the nanometer-sized particles from combining with each other by the self-organizing mechanism, a low concentration of the nanometer-sized particles is exclusively produced in gas phase. This is true, particularly, with respect to nanometer-sized metal particles.
Now, technical terms used herein will be described in detail.    a) Ultradispersed primary particles of nanometer-sized carbon (hereinafter referred to as “nanocarbon”):
Known as the nanocarbon in the prior art are: fullurenes such as C60 fullerene and like fullerenes; carbon nanohorns; carbon nanotubes; nanodiamond; and, primary particles of carbon black. Consequently, the ultradispersed nanocarbon means all the above-mentioned ultradispersed carbon materials.    b) Van der Waals aggregation or an aggregate structure formed by van der Waals forces:
This term means an interparticle aggregate structure formed by van der Waals-London type dispersion forces exerted between atoms and molecules.    c) Detonation-method diamond:
In an inert medium atmosphere, an explosive with a composition containing carbon but no oxygen is detonated without any additional carbon to produce soot in which ultrafine diamond particles are contained in high concentration. Retrieved from such soot is the detonation-method diamond consisting of the ultrafine diamond particles or powder.    d) An agglutinate structure:
Examples of an agglutinate structure is shown in FIGS. 1 and 2, in each of which: an aggregate structure of primary particles wrapped with a plurality of layers of graphite is shown. Such aggregate structure is hereinafter referred to as the agglutinate structure in order to distinguish them from other aggregate structures, for example such as an aggregate structure in which the primary particles of nanocarbon are held together by van der Waals forces. More specifically, in the agglutinate structure of the primary particles, the graphite layers are deposited on surfaces of the primary particles to wrap them. Since graphite is the most stable form in carbon state at room temperature and atmospheric pressure, graphite is deposited on the surfaces of the primary particles when the particles of nanocarbon is prepared by the so-called bottom-up method.    e) Carbon nanohorns:
As shown in FIG. 3a, the carbon nanohorn is a modification of a carbon nanotube which assumes a conical shape. As is clear from FIG. 3a, the nanohorn is extremely short in longitudinal length and available in mass production without using any catalyst. Therefore, the nanohorn has a large number of advantageous applications in use. As is in any one of the other types of fullerenes, this interesting structure of the nanohorn is characterized in the presence of a pentagonal shape in a network formed by a plurality of hexagonal shapes. More specifically, although the nanotube has 6 pieces of the pentagonal shapes in each of its opposite cap portions, the nanohorn has only one cap portion which is provided with 5 pieces of the pentagonal shape. Further, in the nanohorn, due to the reason for geometric requirements of the shape, the nanohorn assuming the conical shape has a vertex angle of 19.2 degrees and is opened in bottom. In practical, it is not possible to obtain the individual nanohorn. An available product of the nanohorns is a dahlia-like covalently-bonded assembly of the nanohorns. In this macro assembly, all the nanohorns have their vertex portions oriented outward.    f) Assembly of the carbon nanohorns:
In the assembly of carbon nanohorns, the carbon nanohorns are assembled into the assembly in a manner different from that of the nanodiamond and carbon black. More specifically, as shown in FIG. 3a, when the primary particles of cone-type carbon nanohorn grow along a peripheral portion of the bottom surface of the cone, the number of dangling bonds increases to make it difficult to supply a sufficient amount of atomic carbon, so that the interparticle combination of the primary particles begins to appears. Due to the influence of their conical shapes, the carbon nanohorns are combined with each other in their head portions so that the nanohorns have their vertex portions oriented always outward. Due to such combination manner, the assembly of the carbon nanohorns keeps on growing until the assembly completes a dahlia-like round bulb shape in its vertex portion radially outwardly extended, as shown in FIG. 3a. The combination of the carbon nanohorns described above forms a structure which is quite different from any other aggregate structure and any agglutinate structure, so that such combination of the carbon nanohorns will be hereinafter referred to as “bonded assembly” of the carbon nanohorns.    g) An assembly:
The assembly means any one of the aggregate structures, the agglutinate structures and the bonded assemblies.    h) Breaking-up, Disagglutination and Decomposition:
These terms mean destruction or separation of the assembly of the primary particles of nanocarbon.    i) Example of the-wet dispersion method corresponding to the wet-type milling method:
Slurry of a powder workpiece is ejected and divided into two jet streams. They undergo a so-called “jet collision”. In the jet collision, the two jet streams of the slurry are subjected to counter collision with each other for pulverization of the workpiece. This process is called the “jet-ejection process”, in which the workpiece is pulverized by its own kinetic energy. There is another pulverization process called the “thin-film process”, in which the slurry of the workpiece is rotated at ultra-high speed. More specifically, in this thin-film process, the slurry is accelerated by a special stirring blade to an ultra-high speed and therefore urged to spread into a thin film over an inner peripheral wall of a rotating tank, so that the powder work piece is effectively subjected to shearing stress exerted by the stirring blade, whereby the workpiece is finely pulverized.
In practice, it is possible to use the wet-type milling method only or in combination with the wet dispersion method.
Now, the reason why the primary particles of nanocarbon are remarkably self-organized will be described.
One of the well-known reasons is the size effect of the nanometer-sized particle (hereinafter referred to as “nanoparticle”) itself. In other words, as the number of atoms disposed in the surface of the particle becomes much lager than that of atoms disposed inside the particle, the surface active properties of the nanoparticle such as absorption, association and reaction remarkably appear. This is particularly true in the most useful material “carbon” in the field of nanotechnology engineering. Since carbon is an atom considerably flexible in valence when combined with other elements or atoms to form a chemical compound or molecule, it is possible for carbon atoms to form a plurality of structures composed of carbon atoms, this complicates the matter. In fact, until recently, the inventors of the subject application have found, through their extensive investigations using a transmission electron microscope (TEM) and/or a the scanning electron microscope (SEM), that all the firm aggregate structures of the primary particles of nanocarbon material fail to exert their own material properties inherent in the material, wherein: the material is manufactured by the so-called “bottom-up” method; and, the investigations are also conducted as to the particle size distribution of the primary particles of the material. It is essential for the today's nanotechnology engineering to establish an effective technique for breaking-up or disassembling the assemblies of the primary particles of nanocarbon.
Technique for manufacturing a diamond particle having a diameter of approximately several tens nm have been already established in the art for abrasive use. These conventional techniques are disclosed in, for example, Japanese Patent application Laid-Open Nos.: Hei 4-132606 (which corresponds to 1992-132606); and, 2002-35636, wherein these conventional techniques are applied to a micron-sized diamond particle having been statically manufactured within the normal range of ambient temperature and pressure, so that the micron-sized diamond particle is ultra-finely pulverized to become an ultra-fine diamond particle. However, the thus obtained diamond particles or powder inevitably includes a diamond particle much larger in size than the micron-sized diamond particle. Furthermore, such larger diamond particle is hard to remove from the pulverized diamond powder. The possible minimum diameter of the thus obtained ultra-fined diamond particles is approximately several tens nm due to the presence of limits inherent in the conventional techniques.
There is also known another conventional method for breaking up the aggregate structure of the primary particles of C60 carried by graphite in large quantities at one step. In the another conventional method: first, the aggregates (which mean the aggregate bodies or structures) of C60 fullerenes in graphite are mixed with both an organic solvent and water to prepare a mixture until C60fullerenes reaches its saturated concentration in this mixture, wherein the organic solvent may be pyridine, tetrahydrofuran or any other suitable solvent; then, a large quantity of water is added to this mixture to prepare a diluted mixture; and, finally, the thus obtained diluted mixture is subjected to an ultrasonic treatment to forcibly remove the organic solvent by vaporization of the solvent to obtain the primary particles of C60 fullerene. However, even in this method, the possible maximum concentration of C60 fullerenes still remains at a value of only 1.4 g/liter (20 mM), as disclosed in a document titled: “Andreivsky, G. V. et al. ; Chem. Phys. Lett.; 2002, 364, 8.”